Thermo Fisher Scientific Demonstrates UHPLC Capabilities with Photodiode Array Detection for Determination of UV Absorbers in Sunscreens

Skin cancer accounts for almost half of all cancers in the US, and more than one million new cases are diagnosed each year. The majority of these cases are associated with exposure to harmful UVB and UVA sun radiation. Sunscreen lotions disperse UV absorbing compounds in an oily base that may also contain emollients, skin moisturizers and light-reflecting particles of zinc oxide. Some of these UV absorbers, such as 4-methylbenzylidene camphor (4-MBC) and octocrylene, may act as endocrine disruptors, which may cause abnormal development of aquatic organisms. Other absorbers, such as octyl-methoxycinnamate (OMC) and homosalate (HMS), have been found to cause significant estrogenic activity, which has been shown to increase growth rates of human breast cancer cells in vitro.

The oily matrix of sunscreen lotions, coupled with the high UV absorbance of the analytes, makes HPLC the method of choice for the analysis of sunscreens. When HPLC is used in conjunction with PDA, it's possible to obtain a complete absorption spectrum for each compound as it elutes. The sensitivity of HPLC/PDA is also sufficient to measure these compounds in water samples, which facilitates research on the potential exposure in water supplies. The new application note describes a UHPLC method for the determination of UV absorbers in sunscreen lotions and in swimming pool water. Also documented is chromatographic method performance including peak resolution, linear calibration range, dynamic range, limits of detection and precision of retention time and peak area.

The UHPLC separation of sunscreen agents presented in the application note provided a six-fold improvement in sample throughput, improved run time from
45 to seven minutes and enhanced resolution and peak shape when compared to traditional analytical methods. Retention time and peak area precision were better than 1 percent RSD, while minimum detection limits obtained with a 1 ?L partial loop injection were on the order of 0.1 - 0.8 mg/L, more than sufficient for the analysis of commercial sunscreen products. The UV absorption spectra collected by the PDA detector provided three important benefits. First, the spectrum of each compound could be stored in a library and later matched with unknown samples to identify and confirm analytes present in a sample. Second, the peak purity index automatically detected poorly resolved peaks, such as degradation products. Finally, the spectrum of each agent clearly identifies it as a UVB, UVA or broad-spectrum absorber.

For more information about the Thermo Scientific Accela high speed chromatography system or to obtain a copy of the application note, please visit www.thermo.com/accela.